The invention relates to the field of array waveguide grating, and in particular a high-index-contrast array waveguide grating photonic integrated circuit.
Rapid growth of high-speed, broadband communication has led to a need to increase the capacity of optical communication networks. Wavelength division multiplexing (WDM) systems have key roles in meeting this need. Such networks require a variety of optical components to enable them to directly process light signals. Planar lightwave circuits (PLCs) fabricated using SiO2-based waveguides are employed in various devices. Of the various types of PLCs, arrayed waveguide gratings (AWGs) are superior to other types of wavelength multiplexers/demultiplexers (MUX/DEMUX), such as dielectric multiplayer filters and fiber Bragg gratings in terms of compactness and large channel number. Thus, 16 to 64 channel AWGs have already been marketed and are widely used as MUX/DEMUX in WDM systems employed in communication networks.
Despite the advantages of AWGs, there are three other fundamental limits on today's AWGs. The first limit is the large footprint. PLCs employ SiO2 materials technologies developed for optical fibers, whose index contrast is less than 1%, referred to as a low-index contrast (LIC) system. The index contrast is defined as (ncore−ncladding)/ncor. While the LIC platform provides a low-loss technology, it necessitates large waveguide bends, typically approximately 1 cm, due to the weak confinement of light. Current AWGs require footprints of about 10×10 cm2.
The second limit is hybrid integration with other optical devices. In order to achieve WDM systems, there is a need to use various devices, such as interleavers, photodetectors, and electronic circuitry. Current integration methods are necessarily hybrid due to the large footprints and thick structures, leading to low production yields and high cost.
The third limit is its thermal instability. Since the bending radii in LIC AWGs are large, the arrayed waveguides are extremely long, typically leading to shifts in the center channel wavelengths. Current SiO2-based AWGs show length changes of 0.011 nm/° C. Thus, thermal controller footprints similar to those of the AWGs are necessary to keep the AWG performances constant.